Control system for machine tool with hydraulically stroked cutter

ABSTRACT

A control system for a machine tool, such as a gear shaper, having a hydro-mechanically stroked cutter spindle, controls the stroking speed of the spindle, the feed of a workpiece relative to a cutter or other tool carried by the spindle, and the pressure of the fluid supplied to the hydraulic portion of the spindle stroking mechanism in such a way as to improve the efficiency of the machine both with regard to the time required to complete a given job and with regard to power consumption. The work force exerted by the spindle during its work stroke may be maintained within a selectable maximum limit and the cutter spindle stroking position is remotely adjustable to bring it into proper working relationship with a workpiece or to raise it to an elevated position to bring it out of working relationship with the workpiece. Various different stroking speeds of the spindle and various different feed rates of the workpiece relative to the spindle are available to suit different job requirements. The control system is also adjustable to adapt it to different stroke lengths and return speed ratios of the spindle.

This is a division of application Ser. No. 758,321, filed Jan. 10, 1977,now U.S. Pat. No. 4,136,302.

BACKGROUND OF THE INVENTION

This invention relates to machine tools having hydro-mechanicallystroked cutter spindles, and deals more particularly with a controlsystem for such a machine.

The control system of this invention, in some or all of its aspects, maybe applied to various different machines wherein a cutter or other toolis carried by a repetitively reciprocated or stroked spindle powered bypressurized hydraulic fluid. An example of such machine is a gear shaperas described in the U.S. patent application of Tlaker and Hazeltinefiled simultaneously with this application. For the purpose of thefollowing description, the machine tool with which the control system isassociated is taken to be such a gear shaper and reference may be had tosaid Tlaker and Hazeltine application for further details of ahydro-mechanical mechanism for stroking the spindle.

The use of a hydro-mechanical means for stroking the spindle of amachine tool permits certain control flexibility not avilable withprevious machines having spindles mechanically driven by linkages, racksand pinions, or the like and the general object of this invention is toprovide a control system taking advantage of this control flexibility toprovide a machine having significant performance and productivityimprovements over prior machines.

Assuming that the machine in question is a gear shaper, such machinerequires the incorporation of certain motions at controlled velocitieswithin certain distances. Some of the important ones of these factorsare: (a) the control of the stroking speed (stroke cycles/minute) of thecutter spindle to permit the cutting of workpieces of various materialsand sizes, (b) the location of the cutter spindle stroking position inproper relationship to the workpiece, (c) the speed at which theworkpiece and cutter spindle are rotated relative to one another toprovide a rotary feed which determines the amount of material removedfrom the workpiece during each cutting stroke of the spindle and resultsin a certain cutting force, and (d) the rate at which the cutter axis ismoved toward or away from the workpiece axis to feed the cutter intocutting depth and the distance it must travel to reach such cuttingdepth. A more particular object of the invention is, therefore, toprovide a control system which conveniently satisfies the needs dictatedby these factors.

In the gear shaper disclosed herein, the hydro-mechanical strokingmechanism is adjustable to provide the cutter spindle with selectivelydifferent stroke lengths and selectively different return speed ratios.A further object of the invention is, therefore, to provide a controlsystem adaptable to accommodate such stroke length and return speedratio changes.

Still other objects of the invention are to provide a control system tocontrol the cutting force exerted by the cutting spindle to eithermaintain the cutting force within a selected maximum limit or tomaintain a constant cutting force during a cutting operation, to controlthe hydraulic supply pressure and flow in response to existing cuttingforce and spindle stroking speeds to converse energy and to protectagainst overspeed and hydraulic failure conditions, to minimize the timerequired for the non-productive return stroke of the spindle, tominimize the time required for the cutter to reach the desired depth cutduring depth feed by providing a variable rate of depth feed whichstarts at a high value and diminishes to a lower value as the toolapproaches the desired depth of cut position, and to provide a cutterspindle positioning means which permits the cutter spindle to bepositioned in response to remote electrical inputs.

Other objects and advantages of the invention will be apparent from thefollowing description and the drawings forming a part hereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a, 1b, 1c and 1d are portions of a complete figure and, when puttogether as shown in FIG. 2, form such a complete figure hereinafterreferred to as FIG. 1, said FIG. 1 being a schematic diagramillustrating a machine tool and an associated control system embodyingthis invention.

FIG. 2 is a diagram illustrating the manner in which FIGS. 1a, 1b, 1cand 1d are oriented relative to one another to form FIG. 1.

SUMMARY OF THE INVENTION

This invention resides in a control system for a machine tool having ahydro-mechanically stroked cutter spindle and the pressure of thehydraulic fluid applied to the spindle driving piston face during thework stroke being detected and used as a cutting foce or load pressureinput signal to the control system. The control system includes meansresponsive to this load pressure signal to maintain the suppliedhydraulic fluid pressure at a value not significantly higher thanrequired for the job at hand. It also includes means for comparing theload pressure signal with a selected cutting force limit signal and tomodify the operation of the machine, if necessary as a result of suchcomparison, to maintain the cutting force at or below the selectedlimit.

The invention resides also in the stroking speed of the spindle beingdirectly related to the speed of a stroking motor and in a means foradding to the signal which controls the speed of the stroking motor, butonly during return strokes of the spindle, a speed increase signal whichincreases the return speed of the spindle to or toward a maximum designreturn speed to thereby since the stroke cycle time and increase theproductivity of the machine.

The invention also resides in the control system including a means forproviding a variable rate of depth feed whereby the depth feed rate ishigh at the beginning of depth feed where cutting conditions are usuallyeasy and whereby the depth feed rate diminishes toward a final or basicrate as the cutting approaches the depth of cut position where cuttingconditions are usually more difficult.

The invention also resides in the control system including an electricalsystem for manually adjusting the work position of the spindle relativeto the workpiece and for elevating the spindle from working relationshipwith the workpiece, the means in question accommodating the fact that asthe spindle stroke length is increased the potential for spindle workposition adjustment is decreased and also accommodating the fact that asthe spindle work position is raised the potential for further elevationof the spindle to bring the cutter out of working relationship with theworkpiece is decreased.

The invention also resides in the control system also providing for thecontrol of hydraulic pressure in response to the rate of reciprocationof the cutter spindle.

DESCRIPTION OF THE PREFERRED EMBODIMENT GENERAL ORGANIZATION

Referring to FIG. 1, the control system of this invention is shownschematically in associated with a machine tool having a verticallyreciprocable cutter spindle 5 carrying a cutter 6 at its lower end. Themovement of the cutter spindle 5 is effected and controlled by ahydro-mechanical system including a servo valve 9, the servo valve beingpart of a servo system operable to valve hydraulic fluid between theillustrated smaller and large piston area chambers 7 and 8 and a drainso that the spindle 5 is slaved to follow the up and down motion of theservo valve. The servo valve 9 is in turn stroked by a stroking linkageor mechanism 11 driven by a stroking motor 10. The stroking linkage 11is such as to produce one cycle of reciprocation of the servo valve 9for each N rotations of the motor 10, and it is manually adjustable tovary both the stroke length and return speed ratio of the servo valve 9,and correspondingly the stroke length and return speed ratio of thespindle 5, the return speed ratio being the ratio of the speed of thespindle or servo valve during its return or up stroke as compared to itsspeed during its down or cutting stroke.

The specific form of the cutter spindle, its hydraulic servo system andthe associated stroking linkage 11 may vary widely without departingfrom the invention. However, in the present instance, these parts aretaken to be those of a gear shaper such as shown in the previouslymentioned patent application filed simultaneously herewith and referencemay be had to said application for further details of such parts.

The cutter 6 and the workpiece may be fed relative to one another byeither or both of a rotary feed drive mechanism 117 powered by a rotaryfeed motor 116 and a depth feed mechanism 167 powered by a depth feedmotor 216. By operation of the rotary feed mechanism, the cutter andworkpiece are both rotated simultaneously about center axes. Byoperation of the depth feed mechanism 167, the center axis of the cutteris moved toward or away from the center axis of the workpiece.

The parts described above comprise essentially the basic machine towhich the control system of this invention applies, and the remainder ofFIG. 1 illustrates the control system itself. The overall control systemin turn is comprised of a number of smaller interrelated systems orsubsystems indicated generally at A, B, C, D and E. System A is astroking control system for controlling the speed of the stroking motor10 to provide various different spindle stroking speeds (strokecycles/minute) and which enables, under favorable circumstances, thespeed of the stroking motor to be increased during the return strokes ofthe spindle to increase the efficiency of the machine by reducing thereturn stroke time.

The system indicated at B is a hydraulic pressure control system whichis responsive to a number of different variables, including actualcutting force, to keep the hydraulic supply pressure above a givenminimum value which varies with stroking speed, but otherwise at a levelno more than needed for the job at hand to conserve energy and yetavoiding excessive forces exceeding the capacity of the machine. It alsofunctions to provide protection against hydraulic pressure failure,excessive stroking speed and excessive supply pressure.

System C controls the rotary feed, through the rotary feed mechanism 117and associated motor 118; and, system D controls the depth feed, throughthe depth feed mechanism 167 and associated motor 216. Both thesesystems are coupled with the stroking motor in such a way as to eachprovide, in one mode of operation, a fixed amount of feed per cuttingstroke of the spindle. These two systems are also coupled with a cuttingforce limit selector 66 and with the hydraulic pressure control system Bin such a manner as to maintain the total feed, whether entirely rotaryfeed, entirely depth feed or combined rotary and depth feed, at such avalue as to keep the actual cutting tool force within the limit set bythe limit selecting means. Lastly, the system E is a system forcontrolling the vertical position of the cutter relative to theworkpiece and for elevating the cutter as, for example, to pass it overworkpiece obstructions.

STROKING SPEED CONTROL

The stroking speed of the cutter spindle 5 and cutter 6 is directlyrelated to the speed of the stroking motor 10 which drives the strokinglinkage or mechanism 11 to mechanically reciprocate the servo valve 9 ata manually adjustable stroke length and at several different manuallyselectable return speed ratios. By way of example, in the illustratedcase, the stroke length is selectively variable, by adjustment of thestroking linkage 11, between a minimum stroke length of one inch and amaximum stroke length of eight inches, and the stroking linkage 11 ismanually adjustable to provide a selected one of three available returnspeed ratios, these being a ratio of 2:1, a ratio of 3:1 and a ratio of4:1.

The stroking speed control system operates to control the speed of thestroking motor 10 and the system indicated generally at A in FIG. 1. Toadjust the control system for changes in the return speed ratio, made byadjusting the stroking linkage 11, the system includes threethree-position switches 14, 17 and 39 the movable contacts of which areganged to operate in unison. Thus, if the stroking linkage 11 isadjusted to provide a 2:1 return speed ratio, the three switches 14, 17and 39 are likewise manually set to their 2:1 ratio positions.Similarly, adjustment of the stroking linkage 11 to provide differentstroke lengths may be compensated for in the control system by threestroke length potentiometers 12, 13 and 15 the wipers of which areganged to move in unison. Thus, if the stroking linkage 11 is set toprovide a six inch stroke length, the wipers of the potentiometers 12,13 and 15 are set to corresponding six inch stroke positions.

The switch 17 provides an output signal MPS establishing a maximumpermissible stroking speed for the particular selected return speedratio in question. As a general rule, as the return speed ratioincreases, the maximum stroking speed of the machine may be reduced, andtherefore, the three resistors connected with the three fixed contactsof the switch 17 are chosen so that the signal MPS reduces as the returnspeed ratio setting selected by the movable contact is increased.

The spindle 5, during its up or return stroke also has a maximum designvelocity which should not be exceeded. The stroking speed correspondingto such maximum spindle return speed velocity is a function of both thereturn speed ratio and the stroke length. A signal SMR representing suchmaximum stroking speed during return stroke of the piston is provided bythe switch 14 and potentiometer 12. For any particular stroking speed,the cutting stroke and return stroke velocities of the spindle will varywith the stroke length, the velocities being high for high strokelengths and low for low stroke lengths. Thus, for long stroke lengthsthe permissible stroking speed, to remain within the maximum designreturn stroke velocity, is less than for short stroke lengths. Thearrangement of the potentiometer 12 is therefore such that the SMRsignal, for any given return speed ratio setting of the switch 14,decreases as the stroke length setting is increased.

The MPS signal and the SMR signal are combined by summing amplifiers 19and 25, inverting amplifier 27 and diode 23 to produce an output signalSM from the amplifier 25 which is equal to SMR if SMR is less than orequal to MPS and which is equal to MPS if SMR is greater than MPS. Thesignal SM is the signal which truly defines the maximum possiblestroking speed, and from the foregoing it will be obserbed that thissignal in turn can never be greater than SMR and therefor can never callfor a stroking speed causing the spindle to be driven at a return speedexceeding the return speed maximum design value. A fundamental strokingspeed signal SS is derived from the maximum speed signal SM by aselector network 16 comprising three potentiometers and three manuallyoperable switches intended to make available three different manuallyselectable stroking speeds. By these means, the basic stroking speedsignal SS may be set to any value equal to or less than SM byappropriately adjusting the wipers of the three potentiometers andselectively closing one of the three associated switches.

If a return speed increase switch 18 is open, the selected strokingspeed signal SS is supplied by itself, through the summing circuit 20and an associated summing circuit 22, the function of which ishereinafter described, to a motor control circuit 24 for driving thestroking motor 10 at a speed directly related to the output from thesumming amplifier 23. The signal SS is constant and, therefore, thestroking motor 10 is driven at a constant speed.

The signal SS corresponds to a stroking speed which is chosen to yield adesired cutter speed during the cutting stroke. But except when SS isequal to SMR, return stroke velocity dictated by the SS signal is lessthan the maximum design return stroke velocity and, to improve theefficiency of the machine the cutter could be driven at a faster returnrate. To obtain such as increase in the return stroke speed, the returnspeed increase switch 18 is closed. When this is done, the signal SMR iscompared with the signal SS by the subtractor 26 which produces anoutput equal to the difference between SMR and SS. This differencesignal is applied to a potentiometer 28 having a wiper driven by a cam29 in unison with the stroking motor 10. The profile of the cam 29 issuch that during the cutting stroke of the spindle and cutter, the wiperof the potentiometer is positioned on ground so that no signal is sentto the summing circuit 20, and therefore the signal supplied to thestroking motor is the basic stroking speed signal SS. During the returnstroke of the cutter, however, the cam 29 positions the wiper of thepotentiometer 28 to pick up some voltage signal which through thesumming circuit 20 is added to the basic stroking speed signal SS toincrease the speed of the stroking motor 10. The profile of the cam 29is further such as to favorably accelerate and decelerate the speedincrease signal during the return stroke movement of the cutter.

CONTROL OF HYDRAULIC SUPPLY PRESSURE

The pressure of the hydraulic fluid supplied to the spindle iscontrolled by the system indicated generally at B. A variabledisplacement pump 30 is driven at a constant speed by a motor 31 and hasits displacement controlled by a controller 52 responsive to anelectrical input signal, the controller 52 operating to cause the pumpto deliver fluid at the rate required by the spindle stroking mechanismand at a pressure dictated by its electrical input signal. The inputsignal to the controller 52, and in consequence the supply pressure ofthe fluid in the supply line 33, is controlled in response to a numberof different variables to keep the supply pressure at a desired value,as discussed below.

The load pressure, that is the pressure of the hydraulic fluid suppliedto the chamber 8 having the piston face of larger area, is monitored bya pressure transducer 32 which produces an analogous output voltage.This analog voltage is sensed during each cutting stroke by a sample andhold circuit 34, as a result of a "sample" signal provided during thecutting stroke by a switch 35 driven by the stroking motor 10, toproduce an output signal P_(L) directly related to the cutting forceexerted by the cutter 6 on the workpiece. The circuit 36 adds a fractionof the P_(L) voltage signal to itself to produce an output signal (P_(L)+CP_(L)) fractionally higher than P_(L).

A pressure transducer 38 monitors the supply pressure and produces anelectrical output signal P_(S) directly related to the supply pressure.

A manually adjustable signal producing circuit 42 produces an outputsignal H designating a selected minimum value below which it is desirednot to have the hydraulic supply pressure fall. Generally, the minimumpressure corresponding to this signal is one below which it is known orbelieved that the machine will not operate properly.

A further signal which influences the supply pressure is a voltage Vdirectly related to the speed of the stroking motor 10 and derived fromthe output of an associated tachometer 44, which output is passedthrough the return speed ratio switch 39 to modify it in accordance withthe selected return speed ratio. The resistors of the switch are chosenso that for any given speed of the motor 10 the signal V is increased asthe switch is set to higher values of return speed ratio and decreasedas the switch is set to lower values of return speed ratio. In anyevent, for any given return speed ratio, the signal V increases withincreases in the spindle stroking speed and acts to increase the minimumsupply pressure with increases in stroking speed.

The signal V is added to the signal H by the summing amplifier 44, toprovide a signal (H+V) which represents the minimum pressure desired forthe particular stroking speed and return speed ratio in question. Thisminimum pressure determining signal (H+V) is combined with the signal(P_(L) +CP_(L)) by the summing and amplifying circuit 45 consisting ofsubtractor 46, diode 48, adder 50, and inverter 51. The output of thesubtractor 46 is (H+V)-(P_(L) +CP_(L)). If (H+V) is greater than (P_(L)+CP_(L)) the output of the subtractor 46 is positive and is passed bythe diode 48 to the summing circuit 50 for summing with the signal(P_(L) +CP_(L)). If (H+V) is less than (P_(L) +CP_(L)), then no signalis passed to the adder 50. As a result, the output of the inverter 51 isa signal P'_(S). If (P_(L) +CP_(L)) is lower than (H+V), then P'_(S)will be equal to (H+V) so as to control the pump 30 through the controlcircuit 52 to maintain the supply pressure at the minimum valuecorresponding to (H+V). On the other hand, if (P_(L) +CP_(L)) is greaterthan (H+V) then P'_(S) will equal (P_(L) +CP_(L)) so that the pump willbe controlled to maintain the supply pressure at a value correspondingto (P_(L) +CP_(L))--that is the supply pressure will be maintained at avalue fractionally higher than the load pressure.

A safety pressure switch 54 is provided to shut down the machine in theevent of excessive supply pressure, but under normal operation, suchexcessive pressure should never be encountered.

From the foregoing, it will be noted that the hydraulic supply systemnormally operates to maintain the supply pressure slightly higher thanthe load pressure and the minimum difference between the two pressureswill be a difference represented by the signal (CP_(L)). If, because ofexcessive stroking speeds or a malfunction of the hydraulic supply unit,this minimum difference is not maintained, an overspeed protectioncircuit comes into play to reduce the speed of the stroking motor torestore the minimum pressure difference. This protective circuitcomprises the subtractor 56 which compares the signal (P_(L) +CP_(L))with the signal P_(S). If the difference between these two signals isless than the desired difference, a signal is sent through the diode 58to the summing circuit 22 where it is combined with the stroking speedcontrol signal appearing on the line 60 to produce a modified strokingspeed control signal slowing the speed of the stroking motor, therebyreturning the stroking speed to a safe value.

The system described above normally operates to maintain at least aminimum value of supply pressure corresponding to the signal (H+V) whichincludes the velocity related component V. To protect against thepossibility of the supply pressure not reaching this minimum value, aprotective circuit comprising the subtractor 62 and diode 64 isprovided. This subtractor 62 compares the signal (H+V), with the signalP_(S) and produces an output signal, which is transmitted to the summingcircuit 22, when P_(S) is less than (H+V), this signal in turn reducingthe speed of the stroking motor. This protective circuit, therefore,protects against hydraulic pressure failure or inadequate hydraulicpressure during idle or low cutting force conditions. It also regulatesmaximum acceleration rates by permitting the stroking speed to beincreased only at a rate compatible with that at which the supplypressure can be raised by the pump 30.

CUTTING FORCE LIMIT CONTROL

Included in the overall control system of FIG. 1 is a means forregulating the maximum cutting force which can be exerted by the tool onthe workpiece. This means includes a manually adjustable circuit 66 forproducing a maximum force limit signal F_(M). This maximum force limitsignal is in turn compared by the subtractor 68 with the signal (P_(L)+CP_(L)) which is directly related to the actual cutting force. If(P_(L) +CP_(L)) is greater than F_(M), then a signal E is produced onthe line 70. When the signal E does appear, it is combined in a sealingcircuit 71 with a feed signal S_(F), derived from the rotary feedcontrol system through contact 211 or from the depth feed control systemthrough contact 212, to produce an excessive load output signal E_(L).The scaler 71 is a multiplier which combines the inputs E and S_(F) inaccordance with the function E_(L) =EFS/C, where C is 10 or some othernumber of similar magnitude. The signal E_(L) is in turn passed to boththe rotary feed drive and the depth feed drive systems to reduce eitheror both feeds and thereby to bring the actual cutting force back towithin the limit set by the circuit 66. That is, if the actual cuttingforce exceeds the maximum limit value established by the circuit 66,then either the rotary feed or the depth feed or both (whichever isbeing used at the time) is modified to slow down the feed rate therebycausing the tool to take a smaller chip and thus reducing the cuttingforce and returning it to an acceptable value.

ROTARY FEED CONTROL

A basic input signal for the rotary feed control system, indicatedgenerally at C, is derived from the stroking motor tachometer 44 and ispassed through a calibration potentiometer 74. The output from thecalibration potentiometer is passed to both a rough cut potentiometer90, through a speed range selector switch 73 and to a finish cutpotentiometer 92 through a fixed resistor 91. The five resistors of thespeed range select switch are of different values. Therefore, thepotentiometer 90 and speed range selector switch provide five differentoutput signals for rough cut operation and the potentiometer 92 andresistor 91 provide a single output signal for finish cut operation.During rough cut operation, the selected rough cut rotary feed signal ispassed on to the point 94 by the switch 96 being closed and the switch98 being open, and during finish cut operation, the signal from thepotentiometer 92 is passed on to the point 94 by the switch 98 beingclosed and the switch 96 being open.

If the machine is being operated at the time without simultaneous depthfeed, then the signal at 94 is passed on to the point 104 by virtue ofthe switch 100 being closed and the switch 102 open. On the other hand,if the machine is being operated with simultaneous depth feed, then theswitch 100 is open and the switch 102 closed so that a reduced value ofrotary feed signal is transmitted to the point 104 because of thereduced feed potentiometer 105.

Finally, if the machine is being operated in an automatic rotary feedmode, then the automatic switch 106 is closed and the manual switch 108opened so as to pass the signal at 104 to the input of the subtractor 76where it is reduced by the output signal E_(L) of the scaling circuit 71in the event that the cutting force at that moment exceeds the valuepreset by the circuit 66.

The output of the subtractor 76 is passed to the rotary feed motorcontrol circuit 110 through a switch 112 dictating reverse or forwardfeed direction, the amplifier 77 being an inverter. If manual rotaryfeed control is desired, the switch 106 is opened, the switch 108 closedand the wiper of the potentiometer 114 manually adjusted to provide acontrol signal for the control circuit 110. The control circuit 110 inturn controls the rotary feed motor 116 having an associated tachometer118 to provide a velocity feedback signal. The rotary feed is activatedor deactivated by the switches 117 and 119, the switch 199 being closedand the switch 117 being opened to activate the feed and the switch 119being opened and the switch 117 closed to deactivate the feed. It willalso be observed from the foregoing that during rotary feed in theautomatic mode, and assuming that no excessive force signal E_(L) isproduced, the selected signal fed to the amplifier 76 is nevertheless,because of ultimately being derived from the tachometer 44, dependent onthe stroking motor speed and therefore a given amount of rotary feedwill be obtained per cutting stroke regardless of the stroking speed.

DEPTH FEED CONTROL

Depth feed, sometimes also called radial feed, is movement of the cutterand workpiece toward each other usually along a line connecting theircenters, to bring the workpiece and the cutter to a center distancesuitable for production of the desired workpiece profile.

In cases where the workpiece is a gear-like object, the depth feed androtary feed are operated simultaneously at preset rates while thereciprocating cutter 6 removes with each cutting stroke an amount ofmaterial determined by their respective rates. The desired depth of cutmay be reached in some instances by using very high depth feed rates andslow rotary feed rates within a very short arc of rotation of theworkpiece or may be reached in other cases by utilizing very slow depthfeed rates and very high rotary feed rates during several revolutions ofthe workpiece. After the desired depth of cut is reached in each case,cutting continues without further depth feed until the workpiece hasrotated an additional 360° to produce the desired profile throughout itscircumference.

The raw control signal for the depth feed system, indicated generally atD in FIG. 1, may be either a stroking speed related signal derived fromthe tachometer 44 through a calibration potentiometer 120 or may be amanually selected nonvelocity related signal derived from a manual input122. The manual input 122 is primarily used for set up purposes.Selector contacts 124 and 125 are used to select between the twooptionally available raw control signals. During a cutting cycle astroking speed related signal is derived from the wiper of potentiometer120 by two potentiometers 126 and 128 optionally selectable by contacts130 and 132. Rate preset potentiometer 126 and contact 130 are used toprovide a basic depth feed signal on line 131 during roughing cuts, andpreset potentiometer 128 and contact 132 are used to provide a basicdepth feed signal on line 131 during finish cuts.

The selected basic depth rate signal may be used either by itself tocontrol the depth feed motor, in which case the feed progresses at aconstant rate regardless of the position of the cutter, or it may beused in conjunction with a subsystem which adds to it an incrementvarying in value with displacement of the cutter from a predeterminedend position, the increment decreasing in value as the cutter movestoward the end position. The subsystem which provides variableaugmentation of the basic depth feed signal may be brought into and outof play by a selector switch 134. When the switch 134 is open, the basicinfeed feed signal passes through the summing circuit 136 by itself, andwhen the switch is closed, the incremental signal provided by thesubsystem is added to the basic signal by the summing circuit. In eithercase, the output of the summing circuit 136 is supplied to a subtractor138, where it is reduced by the signal E_(L) from the sealer 71 of thecutting force limiting circuit, if such signal is present. The signalE_(L) results from the load pressure exceeding the maximum limit valueestablished by the limit selector 66 and scaling circuit 71 and,therefore, in the subtractor 138 the signal E_(L) is subtracted from thedepth feed signal supplied from the summing circuit 136 to reduce thedepth feed rate, thereby reducing the size of chip taken by the tool andaccordingly reducing the load pressure to return it to within the limitpreselected.

The output of subtractor 138 is in turn transmitted to a depth feedpotentiometer drive control 140 which controls a motor 142 having anassociated tachometer 144 for velocity feed back to control 140.

Motor 142 drives the wipers of position feed back potentiometers 168 and169. The output of potentiometer 169 is passed to a depth feed control214 which operates depth feed motor 216 having associated with it atachometer 218 for velocity feed back and position feed back device 220.

Operation of motor 142 changes the wiper position of potentiometer 169which produces an error (command) signal to control 214 andcorresponding rotation of motor 216 which produces depth feed motion.This resultant depth feed motion changes the output of position feedback device 220 to a level sufficient to null the error signal from thepotentiometer 169 in the familiar manner of a null seeking positionservo.

The variable depth feed augmentation subsystem includes a number of endposition defining potentiometers 146, 148, 150 and 152, the output ofany one of which may be chosen and applied to the point 154 by openingand closing in proper combination a number of selector switches 156 to166. In particular, the potentiometer 152 may be set to define theposition of the cutter at the start of a cutting operation. Thepotentiometer 150 may be set to define the position of the cutter at theend of the first cut. The potentiometer 148 may be set to define theposition of the cutter at the end of the second cut, and thepotentiometer 146 set to define the position of the cutter at the end ofthe final cut. A position feedback potentiometer 168 has its wiper movedby the depth feed potentiometer drive motor 142 simultaneously with thewiper of the position input potentiometer 169 so that the voltage signalpicked up by the wiper of the potentiometer 168 defines the actual ormomentary cutter position. All of the potentiometers 146 to 152 and 168are energized by the basic depth feed signal from the line 131 with theresult that the incremental signal provided by the augmentationsubsystem is scaled in accordance with the value of the basic depth feedsignal. That is, if the basic depth feed signal is changed, as byswitching from the roughing rate potentiometer 126 to the finishing ratepotentiometer 128, or by increase of stroking speed, the augmentationsignal is correspondingly increased.

The selected end position signal appearing at the point 154 is suppliedto a subtractor 170, through a potentiometer 173, which compares it withthe actual cutter position signal appearing on the line 172. The outputof the subtractor 170 is an augmentation signal appearing on the line174 which varies in value depending on the difference between the actualcutter position and the desired end position and on the setting of thepotentiometer 173. The net effect is that the augmentation signal willbe relatively high when the cutter is spaced some distance from aselected end point and will decrease in value as the cutter approachessuch end point, the signal becoming zero when the selected end point isreached. The slope of the characteristic line defining the value of theaugmentation signal as a function of cutter displacement from a selectedend point is varied by the potentiometer 173. Accordingly, at the startof a cut, the cutter will be fed at a relatively high depth feed rateand the rate of depth feed will decrease as the cutter reaches the endposition with the feed rate at the end position being a basic(non-augmented) feed rate as dictated by the basic feed rate signal onthe line 131.

The actual cutter position signal from the line 172 and the selected endposition from the point 154 are also supplied to a comparator 176 whichoperates to provide a signal terminating depth feed when the two signalsreach comparison, the output of the comparator 176 being supplied to adepth feed terminating relay 178 which operates contacts 179 for thispurpose. Thus, the depth feed of the cutter is automatically stoppedwhen the selected end position is reached. After the completion of acutting cycle, the wipers of potentiometers 168 and 169 are returned toa starting position defined by the output of potentiometer 152 at a rategoverned by the input voltage supplied from the reset input 222 to thepotentiometer drive 140.

SPINDLE STROKE POSITION AND ELEVATING CONTROL

The machine in question has a housing which carries the spindle 5. Anindex point fixed to the housing may be taken as a housing referencepoint and another index point fixed to the spindle may be taken as aspindle reference point. As the spindle reciprocates the spindle indexhas an average or middle position displaced a given distance from thehousing index. For stroke lengths less than the available maximum, thestroking of the spindle may be varied to change the average position ofthe spindle index relative to the housing index.

Adjustment of the average spindle index position relative to the housingindex may be made for two reasons: First, to bring the stroking motionof the tool into proper position relative to a workpiece during acutting operation and, second to elevate the cutting tool to pass itover workpiece obstructions when moving from one cutting station toanother.

The system for making this adjustment is indicated generally at E inFIG. 1. In particular, adjustment of the displacement of the spindleindex average position from the housing index is performed by asyncro-driver 180 which adjusts an associated part of the strokinglinkage 11. The syncro-driver operates in conjunction with an associatedclamp operated by a solenoid 182, the clamp being released when thesyncro is operated and returned to clamping condition when the syncro isde-energized to hold the adjustable part of the stroking linkage 11 inits new position. A position feedback potentiometer 184 is driven by thesyncro and provides a voltage signal on the line 186 representing theactual position relative to the housing index of the spindle indexaverage position.

The system also includes a first means for adjusting the average spindleindex position during a cutting operation and another means foradjusting the elevated position to which the average index position ismoved upon the actuation of an elevate switch 188. These means include acutting stroke position potentiometer 190 ganged with an elevatedposition potentiometer 192. Both potentiometers are energized by theoutput signals from the ganged potentiometers 13 and 15, which outputsignals vary in accordance with the selected length of cutting toolstroke. That is, for a long selected stroke, little or no stroke lengthis available for adjustment purposes and accordingly little or no signalis sent to the potentiometers 190 and 192 whereas on the other hand,when a short stroke length is chosen, more potential for adjustment isavailable and accordingly a larger signal is sent to the potentiometers190 and 192.

The wipers of the two potentiometers 190 and 192 are ganged to operatein unison and in such a manner, as seen in FIG. 1, that if one wiper ismoved down the other is moved up. Thus, if the cutting stroke positionpotentiometer 190 is adjusted to call for the cutting stroke to occur ata high or up position, in which case there is little or no range leftfor further elevation, the elevated position potentiometer 192 isadjusted to provide a very small or zero signal on its wiper. On theother hand, if the cutting stroke position potentiometer 190 is set tocall for a low cutter position, more possibility for cutter elevationexists and the wiper of the elevation potentiometer 192 is moved to pickup a higher voltage signal. The wiper of the potentiometer 192 in turnfeeds another potentiometer 194 which is manually adjustable to providea signal indicating the degree of elevation desired from the amount ofelevation potential available.

When the elevate switch 188 is open, the output of the cutting strokeposition potentiometer 190 is passed through the summing circuit 196 andis, in the summing circuit 198, subtracted from the output of theposition feedback potentiometer 184. If the two signals do not match,the output from the circuit 198 will be either negative or positive andwill, depending on polarity, energize the relay 202, through inverter201, to energize either the relay 204 to raise the spindle or the relay206 to lower the spindle, until the actual position reaches the dictatedposition. When the elevate switch 188 is closed, an additional signal,dictated by the settings of the potentiometers 192 and 194 is added tothe cutting stroke position signal, in the adding circuit 196, to causethe spindle position to be adjusted upwardly by the amount called for bythe elevate signal. When the elevate switch is released, the elevatesignal is removed and the spindle position is returned to that calledfor by the cutting stroke position potentiometer.

We claim:
 1. The combination in a hydro-mechanically operated machinetool of a repetitively reciprocable work spindle having for each cycleof reciprocation a work stroke and a return stroke, means forreciprocating said spindle including means defining a piston chamber anda valve means, a source of hydraulic fluid supplied at said supplypressure to said valve means, said valve means being operable to connectsaid piston chamber to said source of hydraulic fluid to drive saidspindle during each work stroke, and means for controlling a supplypressure of said hydraulic fluid in response to the pressure prevailingin said piston chamber during work strokes of said spindle.
 2. Thecombination in a hydro-mechanically operated machine tool of arepetitively reciprocable work spindle having for each cycle ofreciprocation a work stroke and a return stroke, means for reciprocatingsaid spindle including means defining a piston chamber to whichhydraulic fluid is supplied to drive said spindle during each workstroke, a source of hydraulic fluid supplied at a supply pressure tosaid spindle reciprocating means, and means for controlling said supplypressure of said hydraulic fluid in response to the pressure prevailingin said piston chamber during work strokes of said spindle, said meansfor controlling said supply pressure of said hydraulic fluid in responseto the pressure prevailing in said piston chamber during work strokes ofsaid spindle including a pressure sensor connected with said pistonchamber for converting the pressure of the fluid in said chamber into ananalogous electrical signal, a sample and hold circuit for sampling theelectrical output from said pressure sensor during only work strokes ofsaid spindle and for producing a load pressure output signal equal tothe sampled values of said pressure sensor output, and means forcontrolling said supply pressure of said hydraulic fluid in response tosaid load pressure signal.
 3. The combination defined in claim 2 furthercharacterized by said means for controlling said supply pressureincluding means for increasing said load pressure signal by a fractionof itself to produce a fractionally increased load pressure signal andmeans for controlling said supply pressure of said hydraulic fluiddirectly in response to said fractionally increased load pressure signalwhereby said supply pressure is maintained at a value fractionallyhigher than the pressure prevailing in said piston chamber during workstrokes of said spindle.
 4. The combination defined in claim 3 furthercharacterized by means for providing a signal representing a pressurebelow which it is desired not to have said supply pressure fall, andsaid means for controlling said supply pressure including means forcontrolling said supply pressure in response to the higher one of saidminimum pressure signal and said fractionally increased load pressuresignal.
 5. The combination defined in claim 4 further characterized bymeans for increasing said minimum pressure signal in response toincreases in the stroking speed of said spindle.
 6. The combinationdefined in claim 3 further characterized by a sensor for sensing saidsupply pressure and for producing an analogous electrical supplypressure signal, and means for reducing the stroking speed of saidspindle in the event said supply pressure signal exceeds saidfractionally increased load pressure signal.
 7. The combination definedin claim 4 further characterized by a sensor for sensing said supplypressure and for producing an analogous electrical supply pressuresignal, and means for reducing the stroking speed of said spindle in theevent said minimum pressure signal exceeds said supply pressure signal.8. The combination in a hydro-mechanically operated machine tool of arepetitively reciprocable work spindle having for each cyle ofreciprocation a work stroke and a return stroke, a tool carried by saidspindle for working on an associated workpiece, means for reciprocatingsaid spindle including means defining a piston chamber to whichhydraulic fluid is supplied to drive said spindle during each workstroke, means providing a electrical load pressure signal directlyrelated to the pressure prevailing in said piston chamber during workstrokes of said spindle, means providing a work force limit signalrepresenting a desired maximum limit for the force exerted by said toolon a workpiece, and means operable in the event said load pressuresignal exceeds said work force limit signal for modifying the operationof said machine to relieve the force exerted by said tool on a workpieceduring work strokes of said spindle and to thereby return said loadpressure signal to a value no greater than said work force limit signal.9. The combination in a hydro-mechanically operated machine tool of arepetitively reciprocable work spindle having for each cycle ofreciprocation a work stroke and a return stroke, a tool carried by saidspindle for working on a workpiece, means for reciprocating said spindleincluding means defining a piston chamber to which hydraulic fluid issupplied to drive said spindle during each work stroke, means forfeeding said spindle relative to a workpiece to feed said tool into saidworkpiece, means providing an electrical load pressure signal directlyrelated to the pressure prevailing in said piston chamber during workstrokes of said spindle, means providing a work force limit signalrepresenting a desired maximum limit for the force exerted by said toolon a workpiece, and means for slowing the rate at which said feed meansfeeds said spindle relative to a workpiece in the event said loadpressure signal exceeds said work force limit signal.